Autism is a developmental disability that typically appears during the first three years of life and affects a person's ability to communicate and interact with others. Dr. Andrew Gerber, a psychiatrists, said that medical experts don't have a comprehensive understanding of what causes autism, but they do know there is a strong hereditary component.

Toxins from the environment could play a role, but currently, data does not support that they do, Gerber said.

Arguments are scheduled to go on throughout the month. A final decision could take several more months to occur. Claims that are successful would result in compensation taking into account lost earnings after age 18 and up to $250,000 for pain and suffering.

The families or the federal government can also appeal the decision of the special master to the Court of Federal Claims or to a federal appeals court.

While there have been about 5,000 claims relating to autism, there have been fewer than 3,000 claims for all other vaccines.

---

On the Net:

Background on thimerosal trial: www.uscfc.uscourts.gov/node/4428